The image deposited on film or a digital sensor is only as good as the image that emerges from the lens. The use of glass or plastic, how many pieces of plastic or glass elements make up the lens, and the precision with which its focusing and zooming mechanisms work all determine the quality and price of a camera. This chapter explains how lenses work so you can use the knowledge to take better pictures.

It’s possible to make a camera that has no lens. It’s called a pinhole camera. You can make one in just a few minutes. All
it takes is a box with a tight-fitting lid that won’t let light in. Punch a small hole—a pinhole, made with a straight pin
or needle—in the center of one side of the box. You can even make a pinhole digital camera by putting a hole in the center
of the body cap that that goes on a camera when its lens is removed. Because light enters the box or the pinhole digital through
such a small opening, it does not spread out and become diffused the way light does, say, entering a room through a window.
The result is a focused image striking the other side of the box. A pinhole camera is not only a fun project, but serious
photographers use it to create excellent photographs. (For more information, including how to build your own pinhole camera,
check out Bob Miller’s Light Walk at http://www.exploratorium.edu/light_walk.)

Pinhole cameras aside, the image deposited on film or a digital sensor is only as good as the image that emerges from the
lens. The use of glass or plastic, how many pieces of plastic or glass elements make up the lens, and the precision with which
its focusing and zooming mechanisms work all determine the quality and price of a camera. The most important function of the
lens is to focus the light entering the camera so that it creates a sharp image when it hits the back of the camera.

You may control the focus by turning a ring running around the barrel of the lens as you check the focus through the viewfinder.
Or you might have nothing to do with it at all. The lens might focus automatically, or it might not change its focus at all.
The cheapest cameras—digital or film—have fixed-focus lenses that bring into definition everything in front of the lens from
a few feet out to infinity. This is not as good a deal as it might seem at first glance. Everything is somewhat in focus,
but nothing is sharply in focus. Plus, a good photographer doesn’t always want everything to be focused. Blurred images have
their place in photography, too.

The lens is not the only player in the focus game. The elements of the exposure system, the image sensor, and the processing
a digital camera does to a picture before depositing it on a memory chip all influence how crisp or mushy the final photo
is.

How Light Works

Photography is all about light—light bouncing off pigments and dyes, light shining through gels and filters, and the shadows
and depth that come with the absence of light. Light is one of the basic influences in life. In fact, it brings life. Without
light there would be no energy on the planet except that lurking deep in its bowels. And yet we’re not exactly sure what light
is. The scientific answers at times contradict each other, and if you start to peer at it too closely, the physical nature
of the universe develops cracks. So we’re not going to do that, but we will look at it in less intimate terms.